The present invention relates in general to combination locks, and more particularly to dial and dial ring assemblies for combination locks having a shielding portion to afford security against unauthorized observation of the combination being dialed when opening the lock.
It is long been recognized that the dialing for combination locks are subjected to theft by unauthorized viewing successive registrations of dial markings occurring during opening of the lock. Where such a lock is opened in the presence of other persons, it is a simple matter for each person to note the combination from a point to the side of or at angles to the rear or over the shoulder of the operator and thereby gain unauthorized access to the vault, safe or other security receptacle protected by the lock. Even where some restriction of the field of view is achieved, persons do not have to see the entire combination dialed at one time, but can learn one number each time the unauthorized observer is able to look at the dial when the combination is being dialed by an authorized person, and thus over a short period of time acquire knowledge of the dialing combination without arousing suspicion of the unauthorized person opening the safe. Ideally, the dial should expose the indicia or numbers of the combination actually being run only to the authorized observer and not anyone standing elsewhere. Heretofore, various expedients have been proposed for use in connection with conventional combination lock dials, which shield the greater portion of the dial from view by unauthorized persons. These are generally taken the form of a shield or cover provided with a window exposing only a limited number of the dial markings to view, either from a direction forwardly of the dial, or in some cases from a direction directly above the dial where the dial markings and numerals are merely provided on a peripheral cylindrical flange surface of the dial. Such dial shields have the dual purpose of hampering observation of the dial numbers by possible surreptitious observance from locations to either side of the operator while the operator is dialing the combination, and limiting the range of exposed dial markings which are visible so that the body of the operator will shield the exposed dial area from observation by person at remote locations to the side of the operator. However, the earlier proposed dial shields where commonly in the form of additional accessories which must be associated with the combination lock and dial, and in many cases afforded such a limited visible dial area that the lock dial must be operated very slowly in order to bring the proper numbers on the dial into registrary with the index mark or zero mark on the dial ring. Also, because of the restricted visible dial area, the numbers are often so obscure or difficult to count that the operator must make a number of attempts before the successful combination is dialed.
U.S. Pat. No. 2,836,052 to Harry C. Miller, U.S. Pat. No. 2,728,215 to Bremer, and U.S. Pat. No. 2,858,692 to Deaton et al., are typical of prior art dial shield arrangements proposed to restrict viewing of the dial numbers during operation of the combination lock dial.
Prior U.S. Pat. Nos. 4,163,376 to Benson L. Miller et al, U.S. Pat. No. 3,968,667 to Klaus W. Gartner et al, and U.S. Pat. No. 4,796,446 to Harry C. Miller et al., all owned by the assignee of the present application, disclose the type of dial shielding facility provided on the dial ring to encircle and shield all but a limited circumferential portion of the cylindrical periphery of a combination lock dial and knob having the dial markings on the cylindrical periphery, as commercially provided by the assignee of the present application for many years, to reduce the change of unauthorized viewing of the combination while it is being dialed by an authorized operator.
An object of the present invention is the provision of a novel combination lock dial and dial ring assembly for combination locks and the like, wherein detenting of the dial relative to the dial ring is provided at a number of equally circumferentially spaced angular positions corresponding to the number of graduation marks on the dial periphery to facilitate exact alignment of the markings on the dial periphery with the fixed index mark on the dial ring and improve the feel of the dial rotation. By thus facilitating exact alignment of the dial markings with the index mark on the dial ring, more precise and accurate setting of the combination during the combination change procedure of the lock is facilitated, so as to avoid combinations being set with the dial being off a portion of a number, which in combination locks built with great precision to minimize surreptitious entry techniques might otherwise cause difficulties in attempted dialing of the proper combination. Also accurate angular positioning of the dial at the proper annular position during dialing of the proper lock-opening combination is facilitated.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.